MainActivity.java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    binding = ActivityMainBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());

    setSupportActionBar(binding.toolbar);

    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
    appBarConfiguration = new AppBarConfiguration.Builder(navController.getGraph()).build();
    NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
    ImageView iv = findViewById(R.id.imageView);

    binding.fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    // Test Hello World From MyOpenCv
    NativeLib cv = new NativeLib();
    System.out.println(cv.stringFromJNI());

    Bitmap image = BitmapFactory.decodeResource(getResources(), R.drawable.android);
    cv.toGrey(image, image);
    iv.setImageBitmap(image);
}